FIG. 5 is an exploded perspective view showing a conventional lens driving device 20 using an electromagnetic drive element.
The lens driving device 20 includes: a lens holder 23 for holding a lens (not shown); a coil 26; a permanent magnet 25; a magnet yoke 21; a base 22; and a spring member 24 being composed of a front spring member 24A and a rear spring member 24B. In this Figure, the photographed object side is set as the positive direction of the Z axis (+Z side, +Z-axis direction or the +Z), the axes that are orthogonal to each other and orthogonal to Z-axis are respectively used as the X axis and Y axis.
A lens is mounted to the lens holder 23 in such way that the optical axis thereof is in the Z-axis direction.
The lens holder 23 includes a cylindrical portion 23a, a front connection portion 23b and a rear connection portion 23c, wherein the cylindrical portion 23a has the shape of a cylinder and orientates the center axis 23A in the Z-axis direction, the front connection portion 23b with annular groove(s) is located on the +Z side of the cylindrical portion 23a, the rear connection portion 23c with annular groove(s) is arranged on the −Z side of the cylindrical portion 23a, a lens (not shown) is held inside the cylindrical portion 23a by the lens holder 23 in such way that the optical axis thereof coincides with the center axis 23A.
The coil 26 winds annularly around the central axis 23A of the lens holder 23, and is attached to the cylindrical portion 23a of the lens holder 23.
The magnet yoke 21 is made of a soft magnetic material, and has a cross section of substantially L-shape. The magnet yoke 21 is composed of a side wall portion 21a and a top surface portion 21b, wherein the side wall portion 21a of a rectangular frame shape extends in the X-axis direction and the Y-axis direction, and the top surface portion 21b of a substantially rectangular plate shape is connected with the +Z side of the side wall portion 21a, and the top surface portion 21b has a circular opening portion 21k open along the Z-axis direction in the central portion thereof. A plurality of (e.g. four) rectangular shaped permanent magnets 25 are mounted in the inner side of the side wall portion 21a of the magnet yoke 21. Permanent magnets 25 are disposed opposite to each other in the X-axis direction and the Y-axis direction respectively about the coil 26, and they are spaced a distance with the side surface formed by the winding of the coil 26.
The base member 22 of a substantially rectangular plate shape has a circular opening portion 22k in the center portion, wherein the board surface thereof faces the Z-axis direction. A restriction portion 22a is formed on the outer portion of the opening portion 22k in X-axis direction and Y-axis direction, it abuts against the rear end portion 23d of the lens holder 23, and restricts the lens holder 23 in the rearmost position of the Z-axis direction. Furthermore, a connection surface 22b is formed on the outside of the restriction portion 22a in the X-axis direction and Y-axis direction, and protrudes in the +Z direction relative to the restriction portion 22a, and connects with the outside holding portion 24b of a rear spring member 24B. Edge portion 22c is arranged on the outermost periphery of the connection surface 22b, and protrudes towards the +Z side relative to the connection surface 22b, and restricts the outside holding portion 24b in a mounting position in the X-axis direction and the Y-axis direction, further, and the rear end portion in the Z-axis direction of the side wall portion 21a is connected to the surface of the +Z side of the edge portion 22c. The spring member 24 is a leaf spring of substantially rectangular shape, which is composed of a front spring member 24A and a rear spring member 24B. The front spring member 24A includes an inside holding portion 24a1, an outside holding portion 24b1 and a plurality of arm portions 24c1, wherein the inside holding portion 24a1 has a circle annular shape, the outside holding portion 24b1 has a rectangular shape, the plurality of arm portions 24c1 are arranged between the inside holding portion 24a1 and the outside holding portion 24b1, and each arm portion 24c1 winds and extends circumferentially and radially, and makes the inside holding portion 24a1 and the outside holding portion 24b1 connected to each other, and each holding portion 24b1 has a curve shape.
The rear spring member 24B is composed of two dividing spring members 241 and 242, and the rear spring member 24B has an inside holding portion 24a2 consisting of one +X side arc-shaped part and another −X side arc-shaped part, and the rear spring member 24B has an outside holding portion 24b2 consisting of one +X side U-shaped part and another −X side of U-shaped part. Each of the dividing spring member 241, 242 includes a plurality of arm portions 24c2, wherein the plurality of arm portions 24c2 each winds and extends circumferentially and radially, which makes the inside holding portion 24a2 and the outside holding portion 24b2 connect with each other, and each has a curve shape. The rear spring member 24B makes one terminal end 261 of the coil 26 connect with the dividing spring members 241 by using solder or the like, and makes the other terminal end 262 of the coil 26 connect with the dividing spring member 242, so as to form the power supply path.
The inside holding portion 24a1 of the front spring member 24A is connected and fixed on the surface of the +Z side of the front connection portion 23b arranged on the lens holder 23, the outside holding portion 24b1 of the front spring member 24A is connected and fixed on the +Z side of the top surface portion 21B of the magnet yoke 21. The inside holding portion 24a2 of the rear spring member 24B is connected and fixed with the surface of the +Z side of the rear connection portion 23c arranged on the lens holder 23, the outside holding portion 24b2 is located in the inner periphery side of the edge portion 22c of the base 22 so as to adjust the position, and is connected and fixed on the surface of the +Z side of the connection surface 22b. 
The spring member 24 is composed of the front spring member 24A and the rear spring member 24B and each has a flat shape extending in the X-axis direction and the Y-axis in a natural state (i.e. the state where the load is not applied) before assembling. However, as shown in FIG. 6 (a)˜FIG. 6(d), when the spring member 24 is assembled with the all kinds of parts, the outside holding portion 24b1, 24b2 relative to the inside holding portion 24a1, 24a2 distorts (offsets) in the −Z direction, thus, the assembling is finished in the state of flexure of the arm portion 24c1, 24c2, and in the state of applying preload in −Z axis direction to the lens holder 23.
Thus, when the coil 26 is not in the energized state, the prepressure in the −Z direction is applied to the lens holder 23 suspended and supported by the spring member 24 mounted on the side of the base 22 due to the restoring force of the arm portion 24c1, 24c2, and the rear end portion 23d of the lens holder 23 abuts against the restriction portion 22a of the base 22.
Furthermore, when the coil 26 is in the energized state, and the Lorentz force in the +Z direction applied onto the coil 26 excesses the prepressure in the −Z direction, the rear end portion 23d of the lens holder 23 departs from the restriction portion 22a of the base 22, the lens holder 23 moves in the +Z direction to a position wherein the restoring force of the arm portion 24c1, 24c2 is balanced.
Patent Document 1: Japan Patent Publication No. 2007-316395
FIG. 6(a)˜FIG. 6(d) are schematic views showing the assembling process of the lens driving device 20.
Referring to FIG. 6 (a), the restriction pin J2a of the spring member mounting jig J2 is inserted into the inner peripheral side of the cylindrical portion 23a of the lens holder 23 with the coil 26 from the +Z side, and the restriction pin J2a is fixed and positioned in such way that the central axis line 23A of the lens holder 23 is aligned with the center of the spring member mounting jig J2. Thereafter, a rear spring member 24B is disposed at the −Z side of the lens holder 23, so that a pressing pressure is applied to the inside holding portion 24a2 in +Z direction from the −Z side, and the rear spring member 24B is connected to the −Z side of the rear connection portion 23c and fixed thereon by adhesive. Then, the terminal ends 261 and 262 of the coil are connected to the spring member 241,242 by soldering or the like.
Subsequently, as shown in FIG. 6 (b), the spring member mounting jig J2 is removed from the cylindrical portion 23a of the lens holder 23, the restriction pin J3a of the base mounting jig J3 is inserted into the inner periphery side of the cylindrical portion 23a of the lens holder 23 from the −Z side. The base 22 is preinstalled in the concave portion J3b of the base mounting jig J3. Center of the base 22 in the X-axis direction and the Y-axis direction is determined due to the restriction of the inner wall surface J3c of the concave portion J3b. 
The rear end portion 23d of the lens holder 23 with the restriction pin J3a of the base mounting jig J3 inserted thereinto abuts against the surface of the +Z side of the restriction portion 22a of the base 22, the lens holder 23 is positioned and holds the lens (not shown) in such way that the center of the base portion 23a of the lens holder 23 is centrally aligned with the restriction pin J3a of the base mounting jig J3. Thereafter, the outside holding portion 24b2 of the rear spring member 24B relative to the inside holding portion 24a2 distorts in the −Z axis so as to restrict the position in the X-axis direction and the Y-axis direction using the edge portion 22c of the base 22, then apply a pressing force in the −Z direction onto the outside holding portion 24b2, at the same time the connection surface 22b of the base 22 is connected and fixed by an adhesive.
Subsequently, as shown in FIG. 6 (c), a magnet yoke 21 installed with a permanent magnet 25 is covered on the base 22 from the +Z side, and the rear end portion in the Z axis direction of the side wall portion 21a is connected and fixed on the surface of the +Z side of the edge portion 22c. The inside holding portion 24a1 of the front spring member 24A is mounted to the surface of the +Z side of the front side connection portion 23b of the lens holder 23 from +Z side, then apply a pressing force of the −Z direction onto the inside holding portion 24a1 from +Z side, at the same time the surface of the +Z side of the front connection portion 23b is connected and fixed by an adhesive.
And then, as shown in 6 (d), apply a pressing force in the −Z axis direction onto the outside holding portion 24b1 so as to make the outside holding portion 24b1 of the front spring member 24A relative to the inside holding portion 24a1 offset in the −Z axis, at the same time the outside holding portion 24b1 is connected and fixed to the surface of the +Z side of the top portion 21B of the magnet yoke 21 by an adhesive or the like.
As shown in FIG. 7, the lens driving device 20 assembled by the above assembly process, when the coil 26 is energized, and the rear end portion 23d of the lens holder 23 departs from the restriction portion 22a of the base 22 and shifts in the +Z axis, an inclination phenomenon often occurs due to the tilt of the lens holder 23.
One reason for generating this phenomenon is that the unwanted residual stress in the direction (X axis direction, Y axis direction) perpendicular to the Z-axis direction is generated on the arm portion 24c2 of the rear spring member 24B. That is to say, the base 22 use the inner wall surface J3c of the concave portion J3b of the base mounting jig J3 as a reference for positioning, and the lens holder 23 uses the restriction pin J3a of the base mounting jig J3 as a reference for positioning. So the center of the lens holder 23 mounted on the base mounting jig J3 and the center of the base 22 are often in the misaligned state. Thus, the outside holding portion 24b2 of the rear spring member 24B is located in the inner side of the edge portion 22c of the base 22, wherein the center of which is in a deviate state.
However, the inside holding portion 24a2 of the rear spring member 24B is fixed on the rear connection portion 23c of the lens holder 23, accordingly, even if the displacement of the outside holding portion 24b occurs, the inside holding portion 24a2 cannot move from the connected rear connection portion 23c. Thus, in order to make the outside holding portion 24b2 of the rear spring member 24B locate in the inner side of the edge portion 22c of the base 22, the outside holding portion 24b2 moves in the X-axis direction and the Y-axis direction for alignment, the outside holding portion 24b2 is eccentric with respect to the fixed inside holding portion 24a2.
As a result, the inside holding portion 24a2 and arm portion 24c2 connected with the outside holding portion 24b2 generate strain in a direction perpendicular to the Z axis, the rear spring member 24B is fixed in a state that the stress towards the direction perpendicular to the Z axis is remained. Further, the lens driving device 20 is assembled in a state that the strain is generated in a direction perpendicular to the Z-axis.
Thus, when the coil 26 is not energized, and stress towards the direction perpendicular to the Z axis is remained on the arm portion 24c2 of the rear spring member 24B, the lens holder 23 under the action of prepressure in the −Z direction of the rear end portion 23d of the lens holder 23 abuts against the restriction portion 22a of the base 22 so as to facing the Z-axis, thus, therefore, the optical axis of the lens (not shown) faces the direction of the photographic direction. However, when the coil 26 is energized, and the lens holder 23 moves up, the stress remained on the arm portion 24c2 of the rear spring member 24B is released, the center of the inside holding portion 24a2 moves towards the center of the outside holding portion 24b2, thereby the lens holder 23 rotates about the axis perpendicular to the Z axis which results in the inclined phenomenon.
When such a tilt of the lens holder 23 occurs, the lens held by the lens holder 23 is also tilt. Therefore, the image of the image sensor (not shown) formed by the tilt lens becomes distorted, the problems, for example, bleeding, blur, image distortion, image quality deteriorated, occurs.
Further, due to during the step of assembling of the rear spring member 24B, the assembling jig is changed from the spring member mounting jig J2 to base mounting member jig J3, so the step becomes complicated, the rear spring member 24B deforms during the jig change, assembly operation time becomes longer, the type of assembling jigs increased, manufacturing costs risen and there are other shortcomings.